The present invention relates to military shelters and more particularly to military shelters of the type which are intended to protect electronic equipment from both normal and abnormal environmental conditions, including severe electromagnetic pulses.
It has previously been known to provide, for military applications, lightweight shelters for protecting and transporting, as a unit, electronic communication systems. Typically, such prior art shelters have comprised panels of the sandwich type which employ inner and outer aluminum skins separated by a lightweight and insulating spacing material, e.g. a foamed plastic or a paper-like honeycomb material. Such panels were typically attached to an aluminum framework using rivets, e.g. of the so-called pop rivet type. The resultant structure, because of the inherently conductive nature of the elements employed, typically provided a degree of electromagnetic shielding, i.e. a form of shielding which would be sufficient to prevent spurious electromagnetic radiations from the equipment installed within the shelter.
Increasingly, however, the military has become concerned with the ability of electronic communications equipment, particularly remote radio relay systems, to withstand the severe electromagnetic pulse which accompanies the high altitude detonation of a nuclear device. As is understood by those skilled in the art, interference with and damage to electronic semiconductor devices can occur, not only from the radiation which accompanies a nuclear explosion, but also from the electromagnetic pulse which is generated by such an event. Induced currents created within the circuits themselves by the electromagnetic wave may, in fact, burn out and destroy a semiconductor device.
In general, prior art shelters have not been deemed in any way satisfactory to prevent this latter kind of damage. At the frequencies of interest, e.g. 200 KHz to 10 GHz, such prior art shelters provide only about 60 db of attenuation of electromagnetic waves. Test results of the present invention indicate a yield of 100 dB of attenuation over this frequency range.
Among the several objects of the present invention may be noted the provision of a novel shelter for protecting electronic equipment from both normal and abnormal environmental conditions, including severe electromagnetic pulses; the provision of such a shelter which can provide electromagnetic wave attenuation in the order of 100 db; the provision of such a shelter which is relatively lightweight and easily transportable; the provision of such a shelter which provides relatively normal ingress and egress capability to permit servicing and operation of electronic equipment therein; the provision of such a shelter which allows adequate ventilation to support personnel working within the shelter; the provision of such a shelter which is relatively easily fabricated and which is of relatively simple and inexpensive construction. Other objects and features will be in part apparent and in part pointed out hereinafter.